Method for crystallizing amorphous silicon thin-film for use in thin-film transistors and thermal annealing apparatus therefor

ABSTRACT

A method for crystallizing an amorphous silicon thin-film is provided, in which amorphous silicon thin-films on a large-area glass substrate for use in a TFT-LCD (TFT-Liquid Crystal Display) are crystallized uniformly and quickly by a scanning method using a linear lamp to prevent deforming of the glass substrate. The crystallization method includes the steps of forming an amorphous silicon thin-film on a glass substrate, and illuminating a linear light beam on the amorphous silicon thin-film from the upper portion of the glass substrate according to a scanning method. The crystallization method is applied to a polycrystalline silicon thin-film transistor manufacturing method including the steps of forming an amorphous silicon thin-film on a glass substrate, and crystallizing the amorphous silicon of the thin-film transistor according to a scanning method using a linear light beam. In the scanning illumination of the linear light beam, either one of a supporting member of the glass substrate and a light source is relatively moved by a scanning driver apparatus.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for crystallizing anamorphous silicon thin-film for use in a thin-film transistor (TFT) anda thermal annealing apparatus therefor, and more particularly, to amethod for crystallizing an amorphous silicon thin-film for a TFT inwhich amorphous silicon thin-films on a large-area glass substrate foruse in a TFT-LCD (TFT-Liquid Crystal Display) are crystallized uniformlyand quickly by a scanning method using a linear lamp to preventdeforming of the glass substrate, and a method for fabricating apolycrystalline TFT using the same, and a thermal annealing apparatustherefor.

[0003] 2. Description of the Related Art

[0004] To enhance driving speed and resolution and improve productivitythrough integration of driving circuits, replacement of amorphoussilicon TFT by polycrystalline silicon TFT is being vividly performedunder study. Difficulties confronting when fabricating a polycrystallinesilicon thin-film are to prevent a deform of glass which is used as asubstrate. To do so, amorphous silicon should be crystallized within atemperature and time at which the glass substrate is resistant withoutbeing deformed.

[0005] A metal-induced lateral crystallization (MILC) method proposed toovercome the above difficulties can lower an amorphous siliconcrystallization temperature at 500° C. or below and has advantages usingsimple equipment and processes compared with other crystallizationmethods. In this MILC method, a metal thin-film such as Ni, Pd and soon, is partially formed on the interface between the surface of anamorphous silicon thin-film and a substrate, and is thermally annealedat 500° C. or so, in such a manner that crystallization proceeds at theportion where the metal thin-film has been formed and in lateraldirection thereof. A polycrystalline silicon TFT can be fabricated usingthe above MILC, in which a device having an excellent electricalcharacteristic can be fabricated at 500° C. or below.

[0006]FIG. 1 is a sectional view showing a manufacturing process of aTFT using the MILC method. As shown, an amorphous silicon thin-film 10is formed in the form of an island on the whole surface of a glasssubstrate 100. Then, a gate insulation film 12 and a gate electrode 13are formed in turn. Then, a metal film 14 of Ni is deposited on thewhole surface of the substrate including a source region 10S and a drainregion 10D and then annealed, to thereby crystallize a channel region10C of the amorphous silicon thin-film 10 by the MILC method.

[0007] The above method has a shorter thermal processing time than thatof a method for forming a gate electrode after depositing andcrystallizing an amorphous silicon thin-film on the whole surface of asubstrate. Since the above method crystallizes only a channel region,yield is considerably improved.

[0008] To crystallize an amorphous silicon by thermal annealing at thestate where the metal thin-film is not formed requires thermalprocessing of about 30 hours at a temperature of 600° C. or above.Meanwhile, the above MILC technique shows a crystallization velocity of1.6 μm/hr or more at 500□□ so, which must be very useful crystallizationmethod. In the MILC method, when a thermal annealing temperature is 600°C. or above, the lateral crystallization proceeds more quickly dependingupon the temperature. Thus, the lateral portions of the portion wherethe metal thin-film has been formed are crystallized all by the MILCmethod.

[0009] Meanwhile, in the case of a next generation large-area glasssubstrate, it does not facilitate to implement a furnace thermalannealing apparatus and it is difficult to enhance productivity becauseof a long-term thermal annealing time. For this reason, a thermalannealing apparatus adopting a number of lamps shown in FIG. 2 has beenproposed.

[0010]FIG. 2 is a sectional view schematically showing a lamp thermalannealing apparatus which is used for crystallization of an amorphoussilicon thin-film according to the conventional prior art. As depicted,a bottom layer oxide film 22 is formed on a substrate 21. A Ni metallayer 24 is formed on the surface of an amorphous silicon thin-film 23formed on the oxide film 22. Then, a process for thermally processingthe amorphous silicon thin-film at high temperature for a second usinglamps 29 and cooling it for five seconds is performed at least once, tothereby crystallize the amorphous silicon thin-film by the MILC method.

[0011] In the MILC method, only an opaque amorphous silicon thin-film isheated and crystallized and a transparent glass substrate is not heatedby the lamps, to accordingly prevent a deformation of the glasssubstrate. The reason for cooling the amorphous silicon for five secondsor so is to block the heats of the heated amorphous silicon from beingtransferred to the glass substrate, in order to prevent deforming of theglass substrate due to the heats transferred from the amorphous siliconto the glass substrate.

[0012] However, the above method for heating the whole surface of thesubstrate is also limited to implement a thermal annealing apparatus foruniformly heating a large-area glass substrate, such as a substrate of600 mm×500 mm or larger. As described above, if all the portions of thesubstrate are not uniformly heated, a thermal processing time should belonger in order to crystallize all the portions of the substrate. Thus,the temperature of the amorphous silicon may be locally raised, so thatthe substrate may be deformed.

SUMMARY OF THE INVENTION

[0013] To solve the above problems, it is an object of the presentinvention to provide an amorphous silicon crystallization method capableof crystallizing an amorphous silicon without deforming a large-areatransparent glass substrate irrespective of the size of the substrate,employing a continuous process rapid thermal annealing (RTA) methodusing light.

[0014] It is another object of the present invention to provide a methodfor manufacturing a low-temperature polycrystalline silicon thin-filmtransistor capable of greatly improving a crystallization uniformity anda crystallization velocity by employing both a continuous process rapidthermal annealing (RTA) method and a metal-induced lateralcrystallization (MILC) method simultaneously.

[0015] It is still another object of the present invention to provide athermal annealing apparatus which is used for crystallization of anamorphous silicon thin-film for use in a thin-film transistor (TFT),capable of preventing deformation of a glass substrate, in which anamorphous silicon thin-film is uniformly and rapidly crystallized on alarge-are glass substrate for use in a thin-film transistor-liquidcrystal display (TFT-LCD) by a continuous process or scanning methodusing a linear lamp.

[0016] To accomplish the above object of the present invention,according to one aspect of the present invention, there is provided athermal annealing apparatus for crystallizing an amorphous siliconthin-film, the thermal annealing apparatus comprising: supporting meansfor supporting at least one glass substrate on which the amorphoussilicon thin-film has been formed; a light source for illuminating alinear light beam to be focused on the glass substrate from the upperportion of the glass substrate; and scanning driver means for relativelymoving one of the supporting means and the light source so that thelinear light beam can be illuminated on the silicon thin-film accordingto a scanning method.

[0017] According to another aspect of the present invention, there isalso provided an amorphous silicon thin-film crystallization methodcomprising the steps of: forming an amorphous silicon thin-film on aglass substrate; and illuminating a linear light beam on the amorphoussilicon thin-film from the upper portion of the glass substrateaccording to a scanning method.

[0018] Also, a method for manufacturing a polycrystalline siliconthin-film transistor employing the above crystallization method,comprising the steps of: forming an amorphous silicon thin-film on aglass substrate; and crystallizing the amorphous silicon of thethin-film transistor according to a scanning method using a linear lightbeam.

[0019] Here, the step of forming the amorphous silicon thin-filmtransistor comprises the sub-steps of: forming an active layer composedof the amorphous silicon on the glass substrate; forming a gateinsulation film and a gate electrode on the active layer in turn; anddepositing a metal thin-film on the resultant glass substrate, whereinthe amorphous silicon with respect to a channel region positioned in thelower portion of the gate insulation film is crystallized by ametal-induced lateral crystallization (MILC) method using the metalthin-film.

[0020] As described above, the thermal annealing apparatus according tothe present invention can locally heat the amorphous silicon to becrystallized by a scanning method where the substrate is transported atthe state where the linearly focused light of the lamp is illuminated onthe glass substrate. As a result, the amorphous silicon can becrystallized without deforming a large-are transparent glass substratesuch as a LCD for a TV irrespective of the size of the substrate andwithout expanding the size of the thermal annealing apparatus on athree-dimensional basis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The objects and other advantages of the present invention willbecome more apparent by describing in detail the structures andoperations of the present invention with reference to the accompanyingdrawings, in which:

[0022]FIG. 1 is a sectional view showing a TFT in order to explain aMILC method;

[0023]FIG. 2 is a sectional view schematically showing a thermalannealing apparatus which is used for transforming an amorphous siliconinto a polycrystalline silicon according to the conventional prior art;

[0024]FIG. 3 is a perspective view showing a thermal annealing apparatusfor crystallizing an amorphous silicon thin-film according to thepresent invention;

[0025]FIG. 4 is a schematic sectional view showing an automatic controlapparatus for controlling a transportation velocity of the substrate inthe FIG. 3 thermal annealing apparatus;

[0026]FIG. 5A is a sectional view of a test piece to be thermallyannealed;

[0027]FIG. 5B is a graphical view showing the temperature slopes of asilicon thin-film at the thermal annealing start step in the cases thata capping oxide film exists or not, respectively;

[0028]FIG. 5C is a graphical view showing the temperature slopes of asilicon thin-film when a metal-induced crystallization (MIC) proceeds atthe thermal annealing intermediate step in the cases that a cappingoxide film is formed or not, respectively;

[0029]FIG. 5D is a graphical view showing the temperature slopes of asilicon thin-film when a metal-induced lateral crystallization (MILC)proceeds at the thermal annealing intermediate step in the cases that acapping oxide film is formed or not, respectively;

[0030]FIG. 6 is a sectional view of the substrate for explaining thetemperature distribution of the substrate and a graphical view of acorresponding temperature distribution when an amorphous siliconthin-film for a TFT according to the present invention is crystallized;

[0031]FIG. 7 is a graphical view illustrating the temperature changeaccording to a time when a thermal annealing is performed according to ascanning method of the present invention;

[0032]FIG. 8 is a graphical view showing the MILC distances at a maximumthermal annealing temperature in the cases that a capping oxide film isformed and not, respectively; and

[0033]FIG. 9 is a graphical view showing the transfer characteristics ofthe polycrystalline silicon TFTs fabricated by he conventional art andthe present invention, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0034] A preferred embodiment of the present invention will be describedin detail with reference to the accompanying drawings. Referring to FIG.3, a thermal annealing apparatus according to the present inventionincludes a halogen linear lamp 35 functioning as a light source 36 forilluminating a light beam 30 focused in linear form on a TFT array 41formed on a glass substrate 40 and an elliptical reflective mirror 34for focusing the light illuminated from the lamp 35 in linear form onthe glass substrate 40. A lower heating portion 31 including a number ofhalogen preheating lamps 32 is fixedly installed in the lower portion ofthe light source 36. A conveyer belt 37 is mounted on the lower heatingportion 31, which functions as a transportation unit for transporting anumber of glass substrates 40 continuously. The conveyer belt 37supports the substrate 40 and simultaneously moves the substrate in onedirection continuously.

[0035] The thermal source, that is, the light source 36 is combined withan automatic control apparatus shown in FIG. 4, to thereby configure acontinuous and uniform heating apparatus. In this case, as the conveyerbelt 37 enables the substrate 40 to move continuously in the arrow markdirection X, the thermal source 36 scans the substrate 40 and performscrystallization of the substrate 40 without excessively heating thesubstrate 40. In this case, the thermal source 36 also movescontinuously by a predetermined distance in the direction opposite tothe arrow mark, to thereby scan the substrate.

[0036] Meanwhile, as shown in FIG. 4, a pair of transmittivity detectionsensors 58A and 58B for detecting transmittivity of the light areinstalled at the back and forth of the thermal source 36. Thetransmittivity data of each portion obtained from the pair of thetransmittivity detection sensors 58A and 58B is supplied to an automaticcontroller 59 for controlling the power of the lamp 35 and thetransportation velocity of the conveyer belt 37 using the transmittivitydata.

[0037] The operation of the thermal annealing apparatus according to thepresent invention will be described below in more detail with referenceto FIGS. 3 and 4.

[0038] A TFT array 41 including an amorphous silicon to be crystallizedis formed on the glass substrate 40 which is put on the conveyer belt 37and transported toward the thermal annealing apparatus. A detectionpattern 42 composed of an amorphous silicon of an elongate strippattern, for monitoring crystallization of the amorphous silicon isformed in one side of the glass substrate 40 along the transportationdirection of the substrate.

[0039] The lower heating portion 31 plays a role of preheating thesubstrate in advance up to a temperature, e. g. 400° C. or below inwhich crystallization of the amorphous silicon does not occur, in orderto shorten a thermal annealing time of the glass substrate 40. The lightbeam 30 generated from the linear lamp 35 of the thermal source 36 islinearly focused by a reflective mirror 34 whose inner circumferentialportion is elliptical and which is formed in lengthy direction to coverthe lamp 35 and illuminated on the glass substrate 40. In this state, ifthe conveyer belt 37 is driven in the arrow direction X, the glasssubstrate 40 continuously moves and is subject to a scanningillumination by the linear light beam 30.

[0040] Thus, it is possible to perform a rapid heating of 80° C./sec ormore by adjusting a scanning condition of the lamp 35. Here, only aheating effect due to conduction of the light beam becomes a singleheating source with respect to the substrate, since cooling air issupplied to the substrate continuously. Accordingly, the transparentglass substrate 40 is not, on the one hand, heated by the lightilluminated from the lamp 35 or the lower preheating lamps 32. On theother hand, the amorphous silicon thin-film of the TFT array 41 formedon the glass substrate 40 absorbs the energy corresponding to thewavelength of the light beam 30 illuminated from the lamp 35 and heatedlocally.

[0041] Meanwhile, at least one lamp 35 can be configured. The array ofthe lamps 35 can be adjusted according to the area of the substrate andthe processing conditions in order to obtain a uniform temperatureslope.

[0042] In the thermal annealing process using the light, the glasssubstrate 40 transmits the light and so is not heated. Thus, only theamorphous silicon absorbs the light to be heated. Here, since theamorphous silicon is transformed into a crystalline silicon which istransparent, a self-stop process for stop a further heating is possible.

[0043] Referring to FIGS. 3 and 4, the detection pattern 42 is alsocomprised of an amorphous silicon. Accordingly, the amorphous silicon ofthe TFT array 41 is transformed into a crystalline silicon and becomestransparent through a crystallization process of the amorphous silicon.A reference numeral 42-1 denotes a portion in which the amorphoussilicon is changed into a crystalline silicon by illumination of thelight beam of the lamp 35 and which has become transparent. A referencenumeral 42-2 is a portion of the opaque amorphous silicon which has notbeen illuminated yet from the lamp 35.

[0044] During crystallization of the detection pattern 42 due toillumination of the light beam 30 from the lamp 35, the preheating lamps32 in the lower heating portion 31 also illuminate the light on thesubstrate 40 to supply an appropriate amount of heat thereto. The lighttransmits through the detection patterns 42-1 and 42-2 to then reach thetransmittivity detection sensors 58A and 58B. Here, the light L1transmitting through the transparent detection pattern 42-1 and thelight L2 whose part is reflected from the detection pattern 42-2 andother part is transmitted through the opaque detection pattern 42-2 aredetected as a respective different value by the transmittivity detectionsensors 58A and 58B according to the difference of the amount of thetransmitted light.

[0045] Then, the automatic controller 59 compares the transmittivityvalues read from each portion of the detection patterns 42-1 and 42-2 bythe transmittivity detection sensors 58A and 58B with a reference valueand judges a thermal annealing state according to the comparison result,to thereby automatically control the operation of each component of thethermal annealing apparatus. That is, the power of the lamps 35 and 32,the transportation velocity of the conveyer belt 37 or thetransportation velocity of the upper thermal source 36 are automaticallycontrolled according to the transmittivity values obtained from thedetection sensors 58A and 58B. Thus, the real-time measurement resultsin the detection sensors 58A and 58B are fed back to the automaticcontroller 59, when the silicon crystallization are not formed uniformlyon the glass substrate 40 during the thermal annealing or the uniformitybetween the processes is changed. As a result, a relative scanningvelocity between the glass substrate 40 and the thermal source 36 and aprocess variable such as a lamp power can be adjusted.

[0046] As the amorphous silicon thin-film is crystallized, transparencyis changed. Thus, if crystallization of the amorphous silicon thin-filmis measured while thermally annealing the large-area glass substrate 40one by one, a process condition can be adjusted in real time. As aresult, the present invention can greatly enhance a crystallizationuniformity compared with a conventional furnace thermal annealing methodwhich thermally annealing a number of large-area glass substrates all ata time.

[0047] The conventional furnace thermal annealing apparatus has atechnical limitation since the size of the furnace becomes larger on athree-dimensional basis as the area of the substrate becomes larger.However, the present invention can solve the above problem byconstructing a two-dimensional expanded heating apparatus, that is,lengthening the linear lamp, in order to heat the large-area glasssubstrate 40. In this case, a scanning apparatus, that is, the conveyerbelt 37 or a thermal source scanning apparatus (not shown) is enough ifa one-dimensional uniformity of the light beam illuminated on the glasssubstrate is maintained although a substrate area increases. Thus, thethermal annealing apparatus of the present invention is veryadvantageous compared with the conventional thermal annealing apparatusrequiring the two-dimensional uniform temperature. The above advantagesare preferably applied to manufacturing of a large-area flat displaysuch as a liquid crystal display (LCD) which is used for a notebook ordesktop computer or a large-sized TV.

[0048] Meanwhile, crystallization of the amorphous silicon at hightemperatures requires a sufficient incubation time. If a thermal processemploying a lamp is used for a MILC, crystallization starts from at aportion where a metal layer is formed and proceeds in lateral directionbefore it reaches an incubation time necessary for crystallization of aportion where the metal layer is not formed. Here, at least one lamp 35can be used in order to enhance a crystallization velocity as describedabove.

[0049] Referring to FIGS. 5A through 5D, a change of the temperatureslopes of the amorphous silicon thin-film are described according to athermal annealing time during thermal annealing using the lamp, in thecases that a capping oxide layer exists or not on the whole surface of atest piece where devices are formed on the glass substrate.

[0050]FIG. 5A is a sectional view of a test piece to be thermallyannealed. FIG. 5B is a graphical view showing the temperature slopes ofa silicon thin-film at the thermal annealing start step in the casesthat a capping oxide film exists or not, respectively. FIG. 5C is agraphical view showing the temperature slopes of a silicon thin-filmwhen a metal-induced crystallization (MIC) proceeds at the thermalannealing intermediate step in the cases that a capping oxide film isformed or not, respectively. FIG. 5D is a graphical view showing thetemperature slopes of a silicon thin-film when a metal-induced lateralcrystallization (MILC) proceeds at the thermal annealing intermediatestep in the cases that a capping oxide film is formed or not,respectively.

[0051] Referring to FIGS. 5B through 5D, a dotted line indicates thetemperature of the silicon region where a capping oxide layer 53composed of SiO2 is deposited on the surface of the transparent glasssubstrate 50 to be thermally processed. The transparent oxide layer 53has an effect increasing the temperature of the amorphous siliconthin-film 51. As such, the thermal processing of the present inventioncan form a capping oxide layer 53 covering the upper portion of theamorphous silicon thin-film 51 in order to enhance the efficiency of theRTA due to the lamp heating. Since the capping oxide layer 53 istransparent, it plays a role of a thermal protection layer for assistingthe light absorption and suppressing the thermal discharging, to therebyincrease a temperature rise effect of only an amorphous silicon.

[0052] The capping oxide layer 53 is also {fraction (1/100 )}the thermalconduction compared with a silicon, which transmits the light of thelamp toward the amorphous silicon thin-film 51 and prevents the locallyheated silicon thin-film from directly contacting the atmosphere and sobeing cooled. Thus, the large-area transparent glass substrate 50 doesnot reach a transformation temperature and only an amorphous siliconthin-film 51 which has been patterned on the substrate 50 is heated upto a temperature necessary for the metal-induced crystallization.

[0053] Referring to FIG. 5A, the test piece has a structure in which anopaque amorphous silicon thin-film 51 is patterned in the form of anisland on the transparent glass substrate 50, an opaque metal thin-film52 having a thickness of 5 Å through 50 Å is partially deposited on theupper portion of the amorphous silicon thin-film 51, and a transparentcapping oxide layer 53 of a thickness of about 3000 Å is deposited onthe whole surface of the test piece.

[0054] Here, the metal thin-film 52 deposited on the upper portion ofthe amorphous silicon thin-film 51 acts as a catalyst for lowering thetemperature of crystallization of the amorphous silicon thin-film 51.The metal thin-film 52 is formed by depositing a metal material such asNi, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Agor an alloy thereof on the amorphous silicon thin-film 51.

[0055]FIG. 5B shows the temperature slopes of a silicon thin-film at thetime when a thermal annealing starts with respect to a test piece. Asindicated, a silicon region A where an opaque amorphous siliconthin-film 51 and a metal thin-film 52 are deposited absorbs a moreamount of light relatively than a transparent substrate region and anamorphous silicon region B where the metal thin-film 52 is notdeposited, and is heated at higher temperatures. Here, the temperatureas indicated in dotted lines in the case that the capping oxide layer 53has been formed is relatively higher than that as indicated in solidlines in the case that the capping oxide layer does not exist.

[0056]FIG. 5C shows the temperature slopes of a silicon thin-film at thethermal annealing intermediate step, in which a metal-inducedcrystallization (MIC) proceeds in lateral direction of the metalthin-film 52. As a result, an amorphous silicon region A positioned inthe lower portion of the metal thin-film is changed rapidly into atransparent crystalline silicon by a metal-induced crystallization(MIC), in such a manner that a light absorption decreases and atemperature falls. Thus, a heat transfer to the substrate is decreased,to thereby decrease the possibility of deformation of the substrate.

[0057]FIG. 5D shows the temperature slopes of a silicon thin-film at thetime when a metal-induced lateral crystallization (MILC) proceeds froman amorphous silicon region A positioned in the lower portion of themetal thin-film 52 where crystallization has been completed according tothe continuous thermal annealing to an amorphous silicon region Bpositioned in the lateral portion of the amorphous silicon region A. Theportion where crystallization has been completed is changed into atransparent crystalline silicon. Accordingly, since a light absorptiondecreases and a temperature falls, it can be seen that the temperatureof the glass substrate 50 is decreased as crystallization of theamorphous silicon proceeds. In FIG. 5D, an arrow mark Z1 indicates adirection in which the MILC proceeds.

[0058]FIG. 8 is a graphical view showing the MILC distances at a maximumthermal annealing temperature in the cases that a capping oxide film isformed and not, respectively, in which a scanning is accomplished at avelocity of 1 mm/sec or so.

[0059] As shown in FIG. 8, a test piece where a capping oxide layer isformed has about five times the crystallization velocity as that wherethe capping oxide layer does not exist, which indicates that atemperature rise effect is obtained by existence of the capping oxidelayer.

[0060]FIG. 6 is a sectional view of the substrate and a graphical viewof a corresponding temperature slope when crystallizing an amorphoussilicon thin-film for a TFT according to the present invention.

[0061] In the case of the TFT, an amorphous silicon thin-film 72 isformed and patterned on a glass substrate 700 and then a gate insulationfilm 73 and a gate electrode 74 are formed thereon. Thereafter, a metalthin-film 75, e. g. a Ni thin-film is deposited in the thickness of 5 Åor more on the whole surface of the glass substrate 700. The metalthin-film 75 is automatically aligned only in a source and drain regionB1 except for a channel region A1 and discriminatively formed.

[0062] In this case, a metal which can be used as a metal thin-film is ametal material such as Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr,Mn, Cu, Zn, Au and Ag except for Ni or an alloy thereof.

[0063] Sequentially, a thermal annealing is performed using a thermalannealing apparatus according to the present invention, in which theamorphous silicon thin-film 72 is crystallized by the MIC and MILCmethods. In this way, since the gate electrode 74 is opaque in the casethat the substrate 700 on which the gate electrode 74 has been formed isthermally annealed, heating is further easily performed by a lamp, toexpediate a MILC method.

[0064] That is, at the initial time, of the thermal annealing operation,the amorphous silicon region B1 (e. g. source and drain regions) coveredwith the metal thin-film 75 and the amorphous silicon region A1 (e. g. achannel region) covered with the opaque gate electrode 74 absorb morelight than a transparent substrate region C1 and are heated at hightemperatures as shown as a solid line. Thereafter, the MIC proceeds andthe amorphous silicon region B1 positioned in the lower portion of themetal thin-film 75 is changed into a transparent crystalline silicon. Asa result, a light absorption rate is decreased, to thereby cause thetemperature to fall down. The MILC also proceeds from the amorphoussilicon region B1 which has been crystallized in the lower portion ofthe metal toward the amorphous silicon region A1 located on the lateralportion of the amorphous silicon region B1. The portion in whichcrystallization has proceeded is changed into a transparent crystallinesilicon. Accordingly, a light absorption rate is decreased, to therebycause the temperature to fall down. In the drawing, an arrow mark Z2indicates a direction toward which lateral crystallization proceeds.

[0065]FIG. 7 is a graphical view illustrating the temperature change ofthe substrate according to a time when a thermal annealing is performedaccording to a scanning method of the present invention. As shown, inthe case of a substrate which has been preheated at 400° C. or so by apreheating lamp, an abrupt temperature rise occurs for several seconds,for example, ten to fifteen seconds when a lamp scans over thesubstrate. By doing so, it can be seen that crystallization is completedand then cooling is performed.

[0066] Thus, deformation of the glass substrate is minimized and aprocess condition appropriate for a large-area continuous process isobtained, by properly adjusting a scanning velocity and a lamp power.

[0067]FIG. 9 is a graphical view showing the transfer characteristics ofthe polycrystalline silicon TFTs fabricated by he conventional art andthe present invention, respectively. The characteristics of the presentinvention and the prior art are measured using a transistor having thestructure shown in FIG. 1. In the present invention, crystallizationwith respect to an amorphous silicon thin-film proceeds according to alinear RTA-MILC method. In the prior art, crystallization proceedsaccording to a furnace MILC method using a furnace thermal annealingapparatus. In this case, when a transistor is thermally annealedaccording to the present invention, a scanning velocity is 1 mm/sec, apreheating temperature of the substrate is 400° C., and the temperatureof a heating line is 700° C. After crystallization has proceededaccording to the present invention and the prior art, thecharacteristics with respect to the TFTs obtained via a generalsuccessive process are investigated. First, a drain current [A] ismeasured according to the change of the gate voltage with respect to theTFT whose drain voltage VD is 5V and width/length (W/L) is 10/8 and thethus-obtained transfer characteristic is shown in the graph of FIG. 9.

[0068] Meanwhile, a threshold voltage M, a sub-threshold slope [mV/dec],a field-effect mobility [cm²/V·s], and a maximum on/off current ratioare shown in the following Table 1. TABLE 1 Item Furnace-MILC RTA-MILCThreshold voltage [V]  1 2.5 Sub-threshold 467 588 slope [mV/dec]Field-effect mobility 120 150 [cm²/V · s] Maximum on/off current 2.8E64.5E6 ratio

[0069] As can be seen from FIG. 9 and Table 1, the physicalcharacteristics of the transistor fabricated by crystallizing anamorphous silicon according to the present invention are substantiallysame as those of a conventional polycrystalline silicon transistor.However, in the case of the on/of current ratio and the field-effectmobility, it can be seen that the values of the transistor according tothe present invention are greatly enhanced.

[0070] As described above, the thermal annealing apparatus according tothe present invention can locally heat an amorphous silicon to becrystallized according to a scanning method where a substrate istransferred at the state where linearly focused lamp light isilluminated on a glass substrate. Accordingly, the present invention cancrystallize an amorphous silicon uniformly without deformation of alarge-area transparent glass substrate such as a LCD for TV irrespectiveof the size of the substrate and without extending the size of thethermal annealing apparatus three-dimensionally.

[0071] Further, in the case where a number of lamps are installed, anamorphous silicon thin-film can be crystallized at a number ofpositions, to thereby enhance a crystallization velocity. Sincecrystallization with respect to an amorphous silicon is controlledindividually and in real-time by an automatic control apparatusincluding a transmittivity detection sensor, the quality of thethermally annealed products can be uniformly maintained, to therebygreatly enhance a yield of large-area LCD products.

[0072] In addition, the method for crystallizing an amorphous siliconthin-film according to the present invention can locally illuminatelinear light on the thin-film using the thermal annealing apparatus, tothereby crystallize the amorphous silicon thin-film uniformly andprevent the substrate from being deformed. Also, in the case that acapping oxide layer, a crystallization velocity can be enhanced.Further, in the case that the present invention is applied tomanufacturing of a polycrystalline silicon transistor, a device havingexcellent physical characteristics can be fabricated without deform ofthe substrate.

[0073] As described above, the present invention has been shown anddescribed with respect to a preferred embodiment as a particularexample. The present invention is, however, not limited to the aboveembodiment, and there are many variations and modifications by a personskilled in the art without departing from the scope and spirit of thepresent invention.

What is claimed is:
 1. A thermal annealing apparatus for crystallizingan amorphous silicon thin-film, the thermal annealing apparatuscomprising: supporting means for supporting at least one glass substrateon which the amorphous silicon thin-film has been formed; a light sourcefor illuminating a linear light beam to be focused on the glasssubstrate from the upper portion of the glass substrate; and scanningdriver means for relatively moving one of the supporting means and thelight source so that the linear light beam can be illuminated on thesilicon thin-film according to a scanning method.
 2. The thermalannealing apparatus according to claim 1 , wherein said supporting meansand said scanning driver means are comprised of a conveyer belt, tosuccessively transfer the glass substrate to the thermal annealingapparatus.
 3. The thermal annealing apparatus according to claim 1 ,further comprising a preheater for preheating the glass substrate fromthe lower portion of the glass substrate.
 4. The thermal annealingapparatus according to claim 3 , further comprising: at least onetransmittivity detection sensor for detecting the transmittivity of thelight illuminated from said preheater to the glass substrate; and acontroller for controlling a scanning velocity of said scanning derivermeans based on the transmittivity data received from said transmittivitydetection sensor.
 5. The thermal annealing apparatus according to claim1 , wherein said controller controls the power of the lamp based on thereceived transmittivity data.
 6. The thermal annealing apparatusaccording to claim 4 , further comprising a detection pattern installedalong the transfer direction of the substrate on one side of the glasssubstrate, which can allow monitoring of a crystallization process ofthe amorphous silicon according to the scanning of the light beam, andsaid transmittivity detection sensor detects the transmittivity of thelight received via the detection pattern.
 7. The thermal annealingapparatus according to claim 6 , wherein said detection pattern iscomprised of an amorphous silicon of a strip pattern.
 8. The thermalannealing apparatus according to claim 1 , wherein said light sourcecomprises: at least one linear lamp disposed in the directionperpendicular to the scanning direction; and a focusing unit forfocusing the light emitted from the linear lamp so that the light isconverged as a linear light beam on the amorphous silicon thin-film. 9.An amorphous silicon thin-film crystallization method comprising thesteps of: forming an amorphous silicon thin-film on a glass substrate;and illuminating a linear light beam on the amorphous silicon thin-filmfrom the upper portion of the glass substrate, according to a scanningmethod.
 10. The crystallization method according to claim 9 , furthercomprising the step of forming at least one metal thin-film pattern forcrystallization induction on the amorphous silicon thin-film.
 11. Thecrystallization method according to claim 10 , wherein said metalthin-film is comprised of one selected from a group composed of Ni, Fe,Co, Ru, Rh, Pd, Os, Ir, Pt, Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag or analloy thereof.
 12. The crystallization method according to claim 10 ,further comprising the step of forming a transparent capping oxide layeron the metal thin film pattern.
 13. A method for manufacturing apolycrystalline silicon thin-film transistor employing the abovecrystallization method, comprising the steps of: forming an amorphoussilicon thin-film on a glass substrate; and crystallizing the amorphoussilicon of the thin-film transistor according to a scanning method usinga linear light beam.
 14. The polycrystalline silicon thin-filmtransistor manufacturing method according to claim 13 , wherein saidstep of forming the amorphous silicon thin-film transistor comprises thesub-steps of: forming an active layer composed of the amorphous siliconon the glass substrate; forming a gate insulation film and a gateelectrode on the active layer in turn; and depositing a metal thin-filmon the resultant glass substrate, wherein the amorphous silicon withrespect to a channel region positioned in the lower portion of the gateinsulation film is crystallized by a metal-induced lateralcrystallization (MILC) method using the metal thin-film.
 15. Thepolycrystalline silicon thin-film transistor manufacturing methodaccording to claim 14 , wherein said metal thin-film is comprised of oneselected from a group composed of Ni, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt,Sc, Ti, V, Cr, Mn, Cu, Zn, Au and Ag or an alloy thereof.
 16. Thepolycrystalline silicon thin-film transistor manufacturing methodaccording to claim 14 , further comprising the step of forming atransparent capping oxide layer on the whole surface of the amorphoussilicon transistor.
 17. The polycrystalline silicon thin-film transistormanufacturing method according to claim 13 , further comprising the stepof preheating the glass substrate at 400° C. or below before scanning ofthe glass substrate due to the linearly heating.
 18. The polycrystallinesilicon thin-film transistor manufacturing method according to claim 14, wherein said glass substrate further comprises a detection patterninstalled along the transfer direction on one side of the glasssubstrate, which can allow monitoring of the crystallization process ofthe amorphous silicon according to the scanning of the light beam,wherein the transmittivity of the light received via the detectionpattern is detected to control the scanning velocity and the power ofthe light beam.